Project Summary Retinal degeneration leading to vision loss is the ultimate outcome of age related macular degeneration (AMD), diabetic retinopathy and glaucoma. Current therapies offer few options to those suffering from late stages of these diseases. In order to explore possible therapies, it is important to use animal models with regenerative capabilities such as the chick embryo. Embryonic chicks regenerate their retina, following retinectomy, via the process of trans-differentiation if exposed to ectopic fibroblast growth factor 2 (FGF2). This process involves the reprogramming of the retinal pigmented epithelium (RPE) to dedifferentiate, losing its pigment, proliferating and forming a neuroepithelium that eventually differentiates to form all major retina cell types. For this proposal, the emphasis will be on the process of dedifferentiation which is key to understanding how transdifferentiation works. Our preliminary data point to a two-step dedifferentiation process where injury (retinectomy) induces the RPE to become competent to respond to FGF2. We have identified a series of factors that are up-regulated with injury only (step 1) including some pluripotency inducing factors (PiFs) and eye field transcriptional factors. In addition, we have found that Lin-28, a PiF and a critical player in Muller glia transdifferentiation in zebrafish, is only up-regulated upon addition of FGF2 (step 2) in the chick eye after retina removal. Based on our preliminary data, we will investigate whether Lin-28 is required and sufficient to induce RPE transdifferentiation in retinectomized chick eyes. We will perform gain-of-function experiments by electroporating a plasmid containing Lin-28 and loss-of-function using morpholinos against Lin28. Our hypothesis is that Lin-28 is sufficient to complete the RPE reprogramming process initiated by injury signals to make new retina. The other focus of this proposal is on dissecting regulatory components including signaling networks and mRNA-miRNA regulatory modules using an unbiased, genome wide approach and taking advantage of state of the art technology such as Next Generation Sequencing to perform mRNA-Seq and miRNA-Seq. We hypothesize that the two-step process implicated in chick RPE dedifferentiation requires a unique set of regulatory molecules at each step. This study will have a significant impact on the field of regenerative medicine since the information obtained can be extrapolated to the process of retina repair in mammals including humans, and specifically on the potential reprogramming of human RPE to generate new neurons. Also the significance of identifying key miRNA molecules that could reprogram RPE is high considering these are small molecules highly desirable for human therapeutics.